Kinematic and non-kinematic passive alignment assemblies and methods of making the same

ABSTRACT

Micromachined passive alignment assemblies and methods of using and making the same are provided. The alignment assemblies are used to align at least one optical element. The alignment assemblies may be configured with kinematic, pseudo-kinematic, redundant or degenerate support structures. One alignment assembly comprises a base and a payload, which supports at least one optical element. The payload may be coupled to the base via connecting structures. The base, the payload and/or the connecting structures may have internal flexure assemblies for preloading a connection, thermal compensation and/or strain isolation.

INCORPORATIONS BY REFERENCE

Co-assigned U.S. patent application Ser. No. 09/855,305, entitled“Angled Fiber Termination And Methods Of Making The Same”, filed on May15, 2001, is hereby incorporated by reference in its entirety.

Another co-assigned U.S. patent application Ser. No. 10/001092, entitled“Optical Element Support Structure And Methods Of Using And Making TheSame”, filed on Nov. 15, 2001, is hereby incorporated by reference inits entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to optical devices, and moreparticularly to optical element alignment assemblies and methods ofmaking the same.

2. Description of the Related Art

An optical component, such as a mirror, lens or fiber, in an opticalinstrument or device, such as an optical switch, should be accuratelylocated/positioned with respect to another optical component in orderfor the optical instrument or device to function properly. Thus, opticaldevices may require their components to be placed with exactingtolerances to fulfill design objectives.

Conventional passive alignment assemblies for MicroElectroMechanicalSystem (MEMS) devices are typically planar in nature and only alignlocal elements, e.g., a fiber and ball lens collimator, where the twocomponents are within a few millimeters of each other. Alignments overlarger distances (e.g., greater than five millimeters), andthree-dimensional optical systems typically use conventionally machinedcomponents. Such assemblies often fail to align optical components withhigh intrinsic precision.

SUMMARY OF THE INVENTION

Components generally need to be located in three dimensions, i.e.,distributed in a volume of space, and have three rotations specifiedand/or controlled. Components located in a plane (two dimensions) withthree or fewer rotations specified and/or controlled are a subset of thegeneral case. Other design objectives may include: (1) locate componentswithout induced strains, either from the process of mounting or throughbulk temperature changes of constituent parts, and/or (2) supportcomponents as rigidly as possible.

In accordance with the present invention, alignment assemblies andmethods of using and making the assemblies are provided. An importantadvantage of several embodiments of the invention is to completelyorient one body with respect to another body to a high degree ofprecision by providing (1) precise mating features between bodies andconnecting elements, and (2) precise distances between these features onall bodies and connecting elements.

In one embodiment, the alignment assemblies are passive, kinematic ornon-kinematic, and micromachined. “Passive alignment” means the variousparts or devices to be assembled have mating features such that whenthese features are engaged with each other, the correct alignment(typically optical) is attained. In some instances, the engagement ofthese mating features permanently controls the alignment. In otherinstances, some type of fixture will hold the parts with their matingfeatures engaged while some additional fixation, e.g., glue or bolt, isadded to make the engagement permanent.

For comparison, in “active” alignment, two parts or devices aremaneuvered with respect to each other by some motion control mechanism,e.g., a motorized motion stage, shim set, etc., in one or moredirections or degrees-of-freedom (DOF) until some metric, e.g., lightthrough-put, optical beam quality, etc., is within a specifiedtolerance. At that point, the two parts are fixed rigidly with respectto each other by some means, e.g., glue, solder, bolt.

As defined and used herein, “kinematic mounting” relates to attachingtwo bodies, which may be called a base assembly or a payload assembly,together by forming a structural path and creating stiffness between thetwo bodies in six, and only six, independent degrees of freedom (“DOFs”)or directions. Each degree of freedom (DOF) kinematically controlledbetween two bodies is also a position defined, i.e., a specific value ofthat DOF, as a linear measurement, may be maintained. Six DOFs aredesired because the location of any object in space is defined by threeorthogonal coordinates, and the attitude of the object is defined bythree orthogonal rotations.

A kinematic support has the advantage of being stiff, yet any strains ordistortions in the base assembly are not communicated to the payloadassembly. Thus, any sensitive optical alignments are not altered in thepayload assembly if the base assembly undergoes deformation due toapplied loads or bulk temperature changes.

In one embodiment, it is desirable to tailor a DOF based on theconfiguration of a “pseudo-kinematic” support. “Pseudo-kinematic” meansthat although there may be many DOFs connecting at least two bodies,such as two micromachined passive alignment assemblies, in a practicalattachment scheme, the DOFs can be tailored such that only six DOFs havea relatively high stiffness, and substantially all other DOFs have arelatively low stiffness.

Thus, true “kinematic” support means only 6 stiff DOFs connecting twoparts, and no other stiffness paths exist. “Pseudo-kinematic” meansthere are 6 DOFs with relatively high stiffness, and possibly many morewith much lower stiffness (typically two to three orders of magnitudeless). In some applications, it is desirable to have pseudo-kinematicDOFs with relatively low stiffness to be two to three orders ofmagnitude lower than DOFs with relatively high stiffness.

DOFs with different levels of stiffness may be accomplished using aflexure system to relieve stiffness in unwanted DOFs. Depending on thecross-sectional properties of elements in the flexure system, connectingelements between two bodies may attain the desired stiffnessconnectivities.

The alignment assemblies and methods of making the assemblies accordingto the invention may provide a number of advantages. For example, themicromachined passive alignment assemblies may be made with highintrinsic precision. Micromachining processes may form three-dimensionalstructures from a substrate wafer with high accuracy. In severalembodiments, one micromachined passive alignment assembly may beoriented and spaced with respect to another assembly (e.g., withconnecting elements) with lithographic precision, e.g.,three-dimensional translational positioning to less than one micron andthree-dimensional angular positioning to less than five arcseconds foran assembly with a 50-mm characteristic dimension.

The methods according to the invention may construct mating surfaces onmicromachined passive alignment assemblies, such as a base assembly anda payload assembly, to control six independent DOFs between theassemblies and allow complete, high-precision specification of positionand attitude. In some applications, it is desirable to havemicromachined connecting elements with counterpart mating surfaces tomate with the mating surfaces on the base and payload assemblies.

The accuracy of micromachined passive alignment assemblies may be fullyrealized if there is a positive contact between a pair of matingfeatures. Thus, some form of preload or force may be applied to maintaincompressive contact between the pair of mating features. An externalforce may be applied to preload mating surfaces to contact each otherprior to gluing. Glues that shrink on cure may be used to maintain thepreload across mating surfaces after assembly.

In addition to or instead of an external force, any of the structuralelements being assembled may have an internal flexure assembly thatapplies an internally-reacted force (preload). The internal flexureassembly may seat mating surfaces without a deadband. In one embodiment,the internal flexure assembly comprises a set of double parallel motionflexures, a preloader stage, and a hole on one side of the preloaderstage for inserting a separate preloader pin. When the preloader pin isinserted into the hole of the internal flexure assembly, the preloaderstage deflects and exerts a force on the pin, which exerts a preloadagainst a mating surface. After the micromachined passive alignmentassemblies are assembled, the mating surfaces may be glued or bonded ifdesired.

A connecting element may be configured to restrain the base assembly andthe payload assembly with one or more desired DOFs. In some embodiments,a “degenerate” support or connecting element may be used where less thansix constrained DOFs between a base and payload are desired. Thedegenerate support may allow some trajectory (i.e., a combination ofCartesian DOFs) of a payload assembly relative to a base assembly to beunconstrained.

A “redundant” support or connecting element may be used in applicationswhere more than six DOFs are desired. The redundant support reinforcesthe base and payload assemblies and maintains their flatness.

As another example, a micromachined passive alignment assembly may havethermal compensation flexure assemblies for maintaining centration ofoptical elements in the presence of large bulk or local temperaturedifferences. The optical elements may then be attached to at least threepads supported by these flexure assemblies to effect this stablepositioning. In some applications, it is desirable to position aplurality of optical elements in a precise pattern in the presence oflarge bulk or local temperature differences. In some of theseapplications, it may be desirable to position a plurality of thermalcompensation flexure assemblies concentric with respect to the center ofan opening and equidistant with respect to each other.

One aspect of the invention relates to an assembly configured to supportat least one optical element to a pre-determined position. The assemblycomprises a first micromachined structure having at least a first matingpart and a second micromachined structure having at least a secondmating part. The second mating part is configured to contact the firstmating part to constrain the second micromachined structure with respectto the first micromachined structure. The second micromachined structureis configured to support at least one optical element.

In one embodiment, the second mating part is configured to contact thefirst mating part to precisely position the second micromachinedstructure with respect to the first micromachined structure. In oneembodiment, the optical element is then precisely positioned withrespect to the first micromachined structure. In one embodiment, thefirst micromachined structure also supports one or more opticalelements.

Another aspect of the invention relates to an assembly configured tosupport at least one optical element. The assembly comprises a firstmicromachined structure having at least a first attachment point and asecond micromachined structure having at least a second attachmentpoint. The second attachment point is configured to contact the firstattachment point to restrain the second micromachined structure withrespect to the first micromachined structure in at least onedegree-of-freedom (DOF). The second micromachined structure isconfigured to support at least one optical element at a predeterminedposition.

In one embodiment, the second attachment point is configured to contactthe first attachment point to restrain and align the secondmicromachined structure with respect to the first micromachinedstructure. In one embodiment, the optical element is then aligned to apre-determined position with respect to the first micromachinedstructure. In one embodiment, the first micromachined structure alsosupports one or more optical elements.

Another aspect of the invention relates to a method of making anassembly configured to position an optical element to a pre-determinedposition. The method comprises using lithography to form a first patternand a second pattern on a substrate for a first structure and a secondstructure. The first pattern outlines a first mating part of the firststructure. The second pattern outlines a second mating part of thesecond structure. The method comprises etching the substrate to form thefirst and second structures according to the first and second patterns.The second mating part is configured to contact the first mating part toconstrain the second structure with respect to the first structure. Thesecond structure is configured to position at least one optical element.

One aspect of the invention relates to an assembly configured to supportat least one optical element to a pre-determined position. The assemblycomprises a micromachined base, a payload and a connecting structure.The base has a first mating part. The payload is configured to positionthe optical element. The payload has a second mating part. Theconnecting structure is configured to contact the first mating part ofthe base and the second mating part of the payload. The connectingstructure constrains the payload in about five to about six degrees offreedom with respect to the base.

In one embodiment, the base also positions an optical element.

Another aspect of the invention relates to an assembly configured toposition at least one optical element to a pre-determined position. Theassembly comprises a base plate and at least one side plate configuredto connect to the base plate. The base plate and the side plate areconfigured to support a plurality of payload plates. Each payload plateis configured to connect to the side plate and to the base plate. Eachpayload plate is configured to position at least one optical element.

Another aspect of the invention relates to a method of making anassembly configured to position at least one optical element to apre-determined position. The method comprises using lithography to forma first pattern, a second pattern and a third pattern on a substrate fora base, a payload and a connecting structure. The first pattern outlinesa first mating part of the base. The second pattern outlines a secondmating part of the payload. The third pattern outlines third and fourthmating parts of the connecting structure. The method further comprisesetching the substrate to form the base, the payload and the connectingstructure according to the first, second and third patterns. Theconnecting structure is configured to contact the first mating part ofthe base and the second mating part of the payload. The connectingstructure constrains the payload in about five to about six degrees offreedom with respect to the base. The payload is configured to positionan optical element.

One aspect of the invention relates to a micromachined flexure assemblyformed in a first structure that is a part of an optical elementalignment assembly. The flexure assembly comprises a set of parallelmotion flexures and a preloader stage coupled to the set of parallelmotion flexures. The set of parallel motion flexures allows thepreloader stage to deflect away from a second structure of the opticalelement alignment assembly and apply a load against the second structureto constrain the second structure in at least one degree of freedom withrespect to the first structure.

Another aspect of the invention relates to a micromachined thermalcompensation flexure assembly formed in a first structure that is a partof an optical element alignment assembly. The flexure assembly comprisesa set of collinear flexures and a center stage coupled to the set ofcollinear flexures. The set of collinear flexures and the center stageare configured to limit distortions in one direction due to atemperature change in the first structure from affecting an opticalelement supported by the first structure.

In one embodiment, three or more such assemblies may completely supporta second structure, e.g., an optical element or assembly, with respectto the first structure such that there are minimal internal stresses,and hence distortions, in the second structure in the presence of bulktemperature changes or substantial temperature differences between thestructures.

Another aspect of the invention relates to a micromachined strainisolation flexure assembly formed in a first structure that is a part ofan optical element alignment assembly. The flexure assembly comprises aset of collinear flexures and a center stage coupled to the set ofcollinear flexures. The set of collinear flexures and the center stageare configured to limit strains in one direction in the first structurefrom transferring to a second structure.

Three or more such assemblies may completely isolate a second structure,e.g., an optical element or assembly, with respect to the firststructure such that there are minimal internal stresses, and hencedistortions, in the second structure in the presence of mechanically orinertially induced distortions in the first structure.

Another aspect of the invention relates to a method of making amicromachined flexure assembly in a structure that is a part of anoptical element alignment assembly. The method comprises usinglithography to form a pattern on a substrate for the structure. Thepattern outlines a set of collinear flexures and a center stage coupledto the set of collinear flexures. The method further comprises etchingthe substrate to form the structure according to the pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a three-dimensional view of one kinematic supportconfiguration.

FIG. 1B is a three-dimensional view of another kinematic supportconfiguration.

FIG. 2A is a side view of a monopod connecting element shown in FIG. 1A.

FIG. 2B is a side view of a bipod connecting element shown in FIG. 1B.

FIGS. 3A-3I are views of slip-fit joint assemblies with opticalelements.

FIG. 4 is a three-dimensional view of another embodiment of a slip-fitjoint assembly.

FIG. 5 is a three-dimensional view of one embodiment of a stiffnesscontrol flexure system and an attachment portion.

FIG. 6 is a three-dimensional view of one embodiment of apseudo-kinematic bipod connecting element.

FIG. 7 illustrates an example of positional control using thepseudo-kinematic bipod connecting element in FIG. 6 attached to a baseassembly and a payload assembly.

FIG. 8 is a side view of one embodiment of an internal flexure assembly.

FIG. 9 illustrates two examples of preloading using a tab and slotattachment scheme with the internal flexure assembly of FIG. 8.

FIG. 10 is a three-dimensional view of one embodiment of a preloaderpin.

FIG. 11 illustrates an example where a plurality of internal flexureassemblies are used to maintain contact at mating surfaces of a slot.

FIG. 12A is a three-dimensional enlarged view of one embodiment of afiber termination array assembly.

FIG. 12B is a three-dimensional assembled view of the fiber terminationarray assembly in FIG. 12A.

FIG. 13 is a side view of two embodiments of redundant connectingelements.

FIG. 14 is a three-dimensional view of the two redundant connectingelements and the plate of FIG. 13.

FIG. 15 is a three-dimensional view of one embodiment of apseudo-kinematic support system.

FIG. 16 is a three-dimensional view of one embodiment of apartially-degenerate support system.

FIG. 17 is a three-dimensional view of another embodiment of apartially-degenerate support system.

FIG. 18 is a three-dimensional view of one embodiment of a strainisolation flexure assembly.

FIG. 19 is a three-dimensional view of one embodiment of a thermalcompensation flexure assembly.

FIG. 20 is a three-dimensional view of one embodiment of a micromachinedpassive alignment assembly with a plurality of chucks in the baseassembly and payload assembly for aligning optical elements.

FIG. 21 is an enlarged three-dimensional view of one part of themicromachined alignment assembly in FIG. 20.

FIG. 22 is a three-dimensional view of one embodiment of an assembly,which comprises a first structure, a plurality of connecting elementsand a second structure.

FIG. 23 is an enlarged view of a redundant attachment point of oneconnecting element in FIG. 22.

FIG. 24 is an enlarged view of a pseudo-kinematic attachment point ofone connecting element in FIG. 22.

FIG. 25 is a three-dimensional view of one embodiment of a megastackstructure.

FIG. 26 is an enlarged view of some attachment points of the side plateand the base plate in FIG. 25.

FIG. 27 is the top view of the megastack structure in FIG. 25.

FIG. 28 is a side view of one embodiment of a side plate in FIG. 25.

FIG. 29 is a three-dimensional view of a complete megastack structure,which is shown partially in FIG. 25.

FIG. 30 is the three-dimensional bottom view of the megastack structurein FIG. 29.

FIG. 31 illustrates one method of designing the three-dimensionalstructures and assemblies described above and translating the designsinto masks for high precision microlithography/photolithography.

FIG. 32 illustrates one method of making high precision,three-dimensional structures described above.

FIG. 33 illustrates one method of assembling three-dimensionalstructures described above from planar parts.

DETAILED DESCRIPTION

FIG. 1A is a three-dimensional schematic view of one kinematic supportconfiguration 100A. The kinematic support configuration 100A in FIG. 1Acomprises a base assembly 102, a payload assembly 104 and six monopodconnecting elements 106A-106F (individually or collectively referred toherein as “monopod connecting element 106”). In one configuration, thebase assembly 102 is a base support structure, and the payload assembly104 holds or aligns an optical element, such as an optical fiber, lensor mirror. The base assembly 102 is connected to the payload assembly104 via the six monopod connecting elements 106A-106F.

Each monopod connecting element 106 in FIG. 1A constrains one degree offreedom (hereinafter referred to as ‘DOF’) between the base assembly 102and the payload assembly 104, as shown by an arrow above the kinematicsupport configuration 100A in FIG. 1A. A constrained DOF may be referredto as a ‘stiff’ DOF or a restrained DOF. The relevant referenceparameter for translational stiffness or translational DOF is force,while the relevant reference parameter for rotational stiffness orrotational DOF is torque.

FIG. 1B is a three-dimensional schematic view of another kinematicsupport configuration 100B. The kinematic support configuration 100B inFIG. 1B comprises a base assembly 102, a payload assembly 104 and threebipod connecting elements 108A-108C (individually or collectivelyreferred to herein as “bipod connecting element 108”). The base assembly102 is connected to the payload assembly 104 via the three bipodconnecting elements 108A-108C. Each bipod connecting element 108constrains two DOFs between the base assembly 102 and the payloadassembly 104, as shown by a pair of arrows near the kinematic supportconfiguration 100B in FIG. 1B. In one embodiment, the kinematic supportconfigurations 100A, 100B each have a structural path between the baseassembly 102 and the payload assembly 104 in six independent DOFs, asshown by the arrows in FIGS. 1A, 1B. Six DOFs of constraint may bedesired for some optic alignment applications.

The kinematic support configurations 100A, 100B in FIGS. 1A and 1B havethe advantage of being as stiff as the connecting elements 106A-106F,108A-108C, but any strain or distortion in the base assembly 102 willnot be transferred to the payload assembly 104 (although a positional orattitude change may occur). Thus, any sensitive optical elements alignedwithin the payload assembly 104 will not be affected if applied loads orbulk temperature changes deform the base assembly 102.

Similarly, if the payload 104 grows or shrinks, there will be no forcestransferred to the base assembly 102 because of the connecting elements106A-106F, 108A-108C. But there may be a change in position or attitudebetween the base 102 and the payload 104. For the symmetric supportconfigurations shown in FIGS. 1A and 1B, the only change is in thevertical direction between the two bodies 102, 104. The payload 104 maybe rigidly supported and maintains position in the presence ofenvironmental conditions, such as inertial loads.

The location of an object in space is defined by three orthogonalcoordinates or vectors, and the attitude of the object is defined bythree orthogonal rotations with respect to the three vectors. Inaccordance with the present invention, if the components of an assembly(e.g., base, payload, and connecting structure such as bipods ormonopods) are formed using an extremely precise fabrication method(e.g., micromachining), then the location and attitude of a payloadrelative to a base may be specified as precisely by fabricatingconnecting structure to calculated dimensions along their support DOF(s)(e.g., a precise length for a monopod, or a precise vertical andhorizontal point of contact for a bipod).

Degenerate Support

If there are fewer than six DOFs constrained between the base 102 andthe payload 104, there may be some trajectory, i.e., combination ofCartesian DOFs, of the payload 104 relative to the base 102 that isunconstrained. In this case, the support between the base 102 and thepayload 104 may be called “degenerate,” and may occur when a connectingelement 106 or 108 is missing or when certain connecting elements 106,108 are parallel. Arbitrarily complex patterns of motion may be createdor controlled by replacing one linear connecting element 106 or 108 witha linear actuator.

Redundant Support

If there are more than six DOFs constrained between the base 102 andpayload 104, and the base 102 distorts or warps, there will be nosolution of payload position and attitude that does not also warp thepayload 104. This type of support may be called “redundant.”

Monopods and Bipods

FIG. 2A is a schematic side view of a monopod connecting element 106shown in FIG. 1A. The monopod connecting element 106 in FIG. 2Aconstrains the base and payload assemblies 102, 104 with point contacts200, 202 at two ends.

FIG. 2B is a schematic side view of a bipod connecting element 108 shownin FIG. 1B. The bipod connecting element 108 in FIG. 2B constrains thebase and payload assemblies 102, 104 with one or more (ideally)frictionless point contacts 204A, 204B at one end and two point contacts206A, 206B at the other end.

The DOFs restrained by the monopod and bipod connecting elements 106,108 are indicated by arrows in FIGS. 2A and 2B. Six monopod connectingelements 106A-106F may constrain six DOFs between the base and payloadassemblies 102, 104, as shown by the arrows in FIG. 1A. Also, threebipod connecting elements 108A-108C may constrain six different DOFsbetween the base and payload assemblies 102, 104, as shown by the arrowsin FIG. 1B.

Both types of joints (point-in-groove joint in FIG. 2A andcircle-in-groove joint in FIG. 2B) may be used interchangeably. Apreload may be used to maintain contact between the base 102, connectingelement 106 or 108 and payload 104 in FIGS. 2A and 2B.

Micromachining

The base and payload assemblies 102, 104 and the connecting elements106A-106F, 108A-108C in FIGS. 1A, 1B, 2A and 2B may be hereinafterreferred to collectively as a “micromachined passive alignment assembly”or a “micromachined assembly.” Other micromachined alignment assembliesare described below. A micromachined assembly may be formed with methodsdescribed below with reference to FIGS. 31-33.

In general, each component in the micromachined assembly in FIGS. 1A,1B, 2A and 2B may be formed by first using a patterning process, such aslithography or photolithography, to form a desired pattern on asubstrate wafer. The substrate wafer may comprise silicon or anothersuitable material, such as gallium arsenide or germanium. Thelithography process may include applying a resist on a surface of asubstrate wafer, aligning a mask with a desired pattern above thesubstrate wafer, exposing the resist to radiation, developing theresist, and hardbaking the resist.

The radiation used for patterning the substrate wafer may include, byway of example, an ultraviolet light, an X-ray beam, or a beam ofelectrons. In one embodiment, the mask is made of a mechanically rigidmaterial that has a low coefficient of thermal expansion. For example,the mask may be made of quartz, borosilicates, metallic chrome, or ironoxide. Patterning may be accomplished using either negative or positiveresists. In some applications, it is desirable to use positive resistswith aspect ratios above unity. In some applications, aphotolithographic process is used to form a desired pattern on thesubstrate wafer. In a photolithography process, a photoresist such asphoto-sensitive film is used in the patterning process.

After developing a pattern on the resist, one or more micromachiningfabrication processes, such as Deep Reactive Ion Etching (DRIE), WireElectric Discharge Machining (Wire EDM or WEDM), LIGA (X-Raylithographie, galvanoformung, und abformtechnik) (X-Ray lithography,electrodeposition, and molding), or SCREAM (Single Crystal ReactiveEtching and Metallization) may be used to etch the substrate waferaccording to the masked pattern. In some applications, it is desirableto etch deep and straight sidewalls in the substrate wafer. In otherapplications, it is desirable to form a three-dimensional structure fromthe patterned wafer.

After etching, the patterned wafer is cleansed. The photoresist and/orresist may be removed using a solvent such as acetone. If there areother fragile MEMs structures on the wafer, a plasma etch may also beused to clean the substrate wafer.

After the fabricated components are cleansed, the components areassembled to form a desired micromachined passive alignment assembly.The fabrication processes described above may be used for making anypart, element, patterned wafer, or component of the micromachinedpassive alignment assemblies described herein. FIGS. 31-33 provideadditional details on micromachining in accordance with the presentinvention.

Slip-Fit Joint

A slip-fit caged joint is a slip-together pair of features which controlat least one DOF in both directions (which may be called “tension” and“compression”), where fit tolerance is added to intrinsic featureaccuracy. Since fit tolerances can be held to 1-3 microns, the tolerancemay be the dominant error. A slip-fit caged joint still forms arelatively high accuracy connection.

FIG. 3A is a three-dimensional view of one embodiment of a slip-fitjoint assembly 300. The slip-fit joint assembly 300 comprises a payloadassembly 302 and a base assembly 304. The payload assembly 302 has threeprotrusions (also called “tabs” or “male connectors”) with matingsurfaces 306A-306C, 308A-308C and 310A-310C (not all mating surfaces arevisible in FIG. 3A). The base assembly 304 has counterpart grooves (alsocalled “slots” or “female connectors”) with mating surfaces 312A-312C,314A-314C, and 316A-316C (not all mating surfaces are visible in FIG.3A).

The mating surfaces 306A-306C, 308A-308C, 310A-310C, 312A-312C,314A-314C, and 316A-316C are configured to engage together. The matingsurfaces 306A, 306C, 308A, 308C, 310A, 310C of the payload assembly 302that are normal to the payload plane are configured to slide past thecorresponding mating surfaces 312A, 312C, 314A, 314C, 316A, 316C of thebase assembly 304. A protrusion such as protrusion 306 and a groove suchas groove 312 control at least two DOFs 324, 326 with a preload as shownin FIG. 3A and described below. A protrusion-groove pair may be called akinematic positioning joint. Each groove has a pre-determined depth,which is less than a height of each protrusion. Each groove isconfigured to contact one of the protrusions and control the protrusionin two degrees of freedom when a preload is applied, as shown in FIG. 3Aand described below. FIG. 3A also shows that each protrusion has foursidewalls, where each sidewall is substantially perpendicular to a planeof the payload 302. Each protrusion has a sidewall facing a center pointof the payload 302.

In one embodiment, there is a fit clearance between the mating surfaces306A, 306C, 308A, 308C, 310A, 310C, 312A, 312C, 314A, 314C, 316A, 316Cto assemble the slip-fit joint assembly 300 of FIG. 3A. In someapplications, it is desirable to have a fit clearance of about 1-3microns For example, the distance between the mating surfaces 312A, 312Cis equal to the distance between the mating surfaces 306A, 306C plus afew microns This fit clearance leads to positioning “slop” or “deadband”of a few microns in (1) the plane of the base assembly 304, which isdefined by two DOFs 318 and 320, and (2) a few arcseconds in rotationabout the normal of the base plane, which is shown as DOF 322. Forrotational DOF 322 in FIG. 3A and other rotational DOFs describedherein, such as DOFs 526, 528 in FIG. 5, the double arrows symbolize arotation about the axis. Each double pair of mating surfaces 306A, 306C,308A, 308C, 310A, 310C, 312A, 312C, 314A, 314C, 316A, 316C in FIG. 3Amay contribute deadband (or free play) that is normal to their surfaces,which is shown as DOF 324.

In one embodiment, a preload is applied to seat the mating surfaces306B, 308B, 310B, 312B, 314B, 316B that are parallel to the payload andbase planes without a deadband in DOF 326. Thus, the position of thepayload assembly 302 normal to the base plane, illustrated as DOF 328,is specifically controlled, as well as the two orthogonal rotationsshown as DOFs 330 and 332, whose axis lie in the base plane. The DOFs328, 330, 332 may be referred to as piston, tip, and tilt.

In embodiment of FIG. 3, the protrusions are square or rectangular inshape, while the female connectors are square or rectangular cavities.In other embodiments, other shapes may be used, such as cylindricalprojections. With cylindrical projections, the restrained DOFs may bethe same as described above, as specified by the base plane pairs 312A,312C, 314A, 314C, 316A, 316C.

FIG. 3B is side view of a payload 302B with three protrusions (similarto FIG. 3A: one Protrusion 306 is shown in FIG. 3B), a base 304B and anoptical element 341, such as a lens. FIG. 3C is a side view and FIG. 3Dis a too view of a payload 302C (similar to FIG. 3A), a base 304C, anoptical element 341, and a hole or receptacle 344, which the same ashole 2002 in FIGS. 20-21 described below.

FIG. 3E is a side view of a payload 302E (similar to FIG. 3A), a base304E, an optical element 351, such as a lens, and a fiber 352. FIG. 3Fis the same as FIG. 3E except the base 304F holds the fiber 352 at anangle, as described in co-assigned U.S. patent application Ser. No.09/955,305, entitled “Angled Fiber Termination And Methods Of Making TheSame” which was incorporated above.

FIG. 3G is a side view of a payload 302 (similar to FIG. 3A), a base304, and a diode 371.

FIG. 3H is a side view of a payload 302H (similar to FIG. 3A), a base304H, and an optical fiber 352.

FIG. 3I is a side view of a payload 3021 (similar to FIG. 3A), a base304I, and an optical element, such as a mirror 380.

FIG. 4 is a three-dimensional view of another embodiment of a slip-fitjoint assembly 400. The slip-fit joint assembly 400 comprises a baseassembly 404 and a payload assembly 402. The payload assembly 402 hasprotrusions 406, 408 and 410 with mating surfaces, while the baseassembly 404 has counterpart recesses 412, 414, and 416 with matingsurfaces. Like the slip-fit joint assembly 300 of FIG. 3, theprotrusions 406, 408, 410 and recesses 412, 414, and 416 with matingsurfaces can engage together like male and female connectors. In thisembodiment, the male connectors 406, 408 and 410 are inverted T-likeprojections, while the female connectors 412, 414, and 416 are windowopenings in the base assembly 404. In FIG. 4, the bottom plane of thebase 404 replaces surfaces 312B, 314B, 316B in FIG. 3, but the base 404provides the same DOF constraints.

The slip-fit joint assemblies 300 and 400 in FIGS. 3 and 4 may befabricated with the same manufacturing procedures described above andbelow with reference to FIGS. 31-33. For example, the lithographyprocess and the micromachining process may fabricate the desired matingsurfaces 306A-306C, 308A-308C, 310A-310C, 312A-312C, 314A-314C,316A-316C of the male and female connectors. In some applications, it isdesirable to include a metallization process after the substrate waferis cleaned. A metal is deposited via sputtering onto the male (tabs) andfemale connectors (slots). The metallization process increasesrobustness and reduces debris formation at the mating surfaces of themale and female connectors.

In one embodiment, each element in an assembly is kinematicallysupported with respect to all other elements. If each connecting element(e.g., element 106 in FIG. 1A) is kinematically supported in addition tothe base and payload, the DOFs controlled by the connecting elements arecapable of more accurate positioning. Thus, there are no allowedtrajectories of the connecting elements (degenerate support). An allowedtrajectory (change of attitude) of a connecting element could disturbthe desired DOF controlled by the connecting element. Also, there is nooverconstraint (redundant support) that could warp the connectingelements. An overconstraint could change a controlled DOF positionthrough applied strain. As a consequence of kinematic support, everystructural element in an assembly can now be a “payload,” which couldsupport one or more optical components to the same levels of accuracypreviously described.

In addition, an unlimited number of structural elements may be attached(to form a “daisy chain”) in this manner to a high level of accuracy.Each successive payload may be the base for the next payload in thechain. Another valid topology is to have an unlimited number of payloadsattached to one set of connecting elements using the same DOFs at eachconnecting element (see “megastack” in FIG. 25). Other topologies may bepossible.

Pseudo-Kinematic Connecting Element, Flexure Systems, Ball Joints,Attachment Points

FIG. 5 illustrates a three-dimensional view of one embodiment of apseudo-kinematic connecting element flexure system and an attachmentpoint 500. “Pseudo-kinematic” means that although there may be many DOFsconnecting at least two bodies through a plurality of connectingelements, such as two micromachined passive alignment assemblies, in apractical attachment scheme, the DOFs can be tailored such that only sixDOFs have relatively high stiffness, and substantially all other DOFshave relatively low stiffness. In some applications, it is desirable tohave at least one DOF with low stiffness to be two to three orders ofmagnitude lower than a DOF with high stiffness. DOFs with differentlevels of stiffness may be accomplished using a flexure system, such asthe flexure system 504 in FIG. 5, to relieve stiffness in unwanted DOFs.Hereinafter, “kinematic” may be used to refer to pseudo-kinematicattachments.

In FIG. 5, the pseudo-kinematic connecting element flexure system andattachment point 500 comprises a body 502, a flexure system 504, and anattachment portion 506. The flexure system 504 couples the body 502 tothe attachment portion 506. The attachment portion 506 and the flexuresystem 504 may be collectively referred to herein as a “ball joint,” a“ball joint flexure” or a “flexured ball joint” in a planar structure. Aball joint is a useful pseudo-kinematic structure that is relativelystiff in substantially all translations and relatively soft insubstantially all rotations.

One embodiment of the attachment portion 506 in FIG. 5 comprises amounting tab 508 with mating surfaces (contact surfaces) 510A, 510B,510D, 510E, which may provide high precision dimensional control tomating elements. The flexure system 504 comprises two flexure elements512, 514 that form a bipod-like structure. Each flexure element 512, 514is very stiff in at least an axial direction. Thus, each flexure element512, 514 provides a very stiff connection between the attachment portion506 and the body 502 in DOFs 516 and 518, as shown in FIG. 5.

Depending on the cross-sectional properties of the flexure system, theconnecting elements may have compliant (or “soft”) rotations becomestiff and tiff translations become soft. The cross-sectional propertiesof the flexure elements 512, 514 include blade depth 520, blade length522, and blade thickness 532. If the blade depth 520 of the flexureelements 512, 514 is significantly smaller (e.g., less than {fraction(1/10)}) than the blade length 522, the attachment of the body 502 tothe attachment portion 506 by the flexure elements 512, 514 may have twostiff DOFs 516, 518 (i.e., forming a bipod), and other relatively softerDOFs 524, 526, 528, 530.

In other applications, if the flexure elements 512 and 514 have a bladedepth 520 that is significant (e.g., greater than about {fraction(1/10)} of the blade length 522), then DOF 524 has significantstiffness, and the attachment has the properties of a ball joint. Therotational DOFs 526, 528 may become stiffer compared to DOF 530, whichis primarily controlled by the flexure blade width 532. In oneembodiment, DOFs 526, 528 are soft and DOF 530 is very soft compared toDOFs 516, 518. Depending on the exact magnitude and the sensitivity of aparticular design, the soft DOFs 526, 528 may not cause any problems.

The stiffness of DOFs is highly dependent on the exact cross-sectionalproperties (blade depth 520, length 522, and thickness 532) of theflexure elements 512, 514. It would be relatively easy to make the“soft” rotational DOFs 526, 528 stiffer and make the “stiff” translation524 softer by changing the cross-sectional properties. As long as theblade length 522 is much greater than the blade depth 520 and the bladethickness 532, e.g., 10 to 1 ratio (other ratios may be used), the “verystiff” translations 516 and 518 and the “very soft” rotation 530 willremain unchanged for this configuration.

In one configuration, it is desirable to have a ball joint at both endsof the body 502 to form a monopod connecting element (not shown). Thisconfiguration would create an appropriate set of stiff DOFs to make themonopod connecting element act like a single DOF constraint between twobodies.

Pseudo-Kinematic Bipod Connecting Element

In another configuration, it is desirable to have three attachmentportions, similar to the attachment portion 506, coupled to the body 502to form a pseudo-kinematic bipod connecting element, as shown in FIG. 6.

FIG. 6 is a three-dimensional view of one embodiment of apseudo-kinematic bipod (i.e., two-DOF support) connecting element 600.The pseudo-kinematic bipod connecting element 600 comprises attachmentpoints 602, 604, 606 and a body 608. The two attachment points 602 and604 of the connecting element 600,may connect to a base assembly (notshown). The attachment point 606 may connect to a (nominal) payloadassembly (not shown).

Two of the attachment points 602 and 606 are coupled to the bipod body608 via ball joint flexures, as described above with reference to FIG.5. The ball joint at attachment point 602 provides three DOFs 610, 612,614 of connectivity to the body 608. The ball joint at attachment point606 provides three DOFs 616, 618, 620 of connectivity to the body 608.The attachment point 604 connects to the bipod body 608 via a singleflexure 622 that provides two DOFs of connectivity 624 and 626.

In one embodiment, three bipod connecting elements, such as the element600 in FIG. 6, are kinematic in their attachments to a base and apayload. The three bipod connecting elements also form a kinematicattachment between a base and a payload.

In FIG. 6, the pseudo-kinematic bipod connecting element 600 “borrows”several DOFs 610, 612, 614, 616, 624, 626 from the base assembly and thepayload assembly to control the position and attitude of the bipodconnecting element 600. This set of DOFs 610, 612, 614, 616, 624, 626forms a 3-2-1 support structure (3 DOFs at one point, two DOFs atanother, one DOF at a third) that is kinematic or pseudo-kinematic.Thus, the pseudo-kinematic bipod connecting element 600 could itself bean optical bench. The remaining DOFs 618 and 620 are used by thepseudo-kinematic bipod connecting element 600 to control the payloadassembly.

The DOFs 610, 612, 614, 616, 618, 620, 624 and 626 may depend on one ormore assumptions described above. For example, it may be assumed thatthe payload assembly is fully constrained by other pseudo-kinematicbipod connecting elements 600. Otherwise, the “borrowed” DOF 616 may notbe constrained.

As another example, at each attachment point 602, 604, 606 connected toa base or payload, all six DOFs with the attached body may beconstrained by an adhesive or a preload (discussed below) to seat themating surfaces without a deadband. The flexure structures may thenselect a subset of these DOFs to connect (i.e., be stiff in) to the body608 to create the kinematic condition.

The structures described herein may have high stiffness in certain DOFsand much lower stiffness in all other DOFs. Some DOFs may vary in acommon fashion with changes in flexure system dimensions, possiblyrequiring that a design decision may be made between either (1) allowingextra stiff DOFs, where an attachment may no longer be pseudo-kinematic,or (2) allowing a desired stiff DOF to be soft, which leaves theassembly with a relatively low frequency vibration mode and any desiredpositional accuracy in that direction may be compromised. Each of thetwo choices may be a viable design. An extra stiff DOF means a redundantsupport, which may be undesirable for an optical bench connected to apoorly-controlled external structure, but may be acceptable for certainsize scales or sets of assumptions. Low frequency vibration modes may bea problem, but if the low frequency is in the kilohertz range while thedevice operates in approximately the 100-Hertz range, there will not bea detrimental dynamic interaction.

The connecting elements 500 and 600 in FIGS. 5 and 6 may be fabricatedwith micromachining manufacturing methods described herein. For example,lithography and micromachining can fabricate the connecting elements 500and 600 to the sub-micron level. To translate these highly accurateplanar processes to highly accurate three-dimensional positioningaccuracy requires the same DOF control used for kinematic attachment. Inother words, the stiff constrained directions used to form a kinematicattachment (e.g., the directions constrained between a base and apayload by three bipod connecting elements) can also have aprecisely-determined dimension associated with each of them, therebyuniquely and precisely specifying the position (translations) andattitude (rotations) between two bodies (e.g., a base and a payload).This precisely-determined dimension is shown in detail below in FIG. 7for one bipod element.

FIG. 7 illustrates an example of the pseudo-kinematic bipod connectingelement 600 (alignment features on a planar object) in FIG. 6 attachedto a base assembly 702 and a payload assembly 704. The attachment points602, 604 and 606 engage into the base assembly 702 and the payloadassembly 704 at the mating surfaces 706A, 706B, 706D, 706E, 708A, 708B,708D, 708E and 710A, 710B, 710D, 710E, respectively. The bipodconnecting element 600 has two constrained and precisely specified DOFsat the payload 704 (DOFs 618 and 620 in FIG. 6).

One alignment feature in FIG. 7 may be a precise separation distance 712between the base assembly 702 and the payload assembly 704, which isdefined by a midpoint 714 of a line formed by mating surfaces 706A and706E of attachment point 602 and another midpoint 716 of a line formedby mating surfaces 710A and 710E of attachment point 606. This preciseseparation distance 712 precisely specifies the location of the payloadassembly 704 relative to the base assembly 702 in the vertical direction(DOF 620 from FIG. 6) at the point of attachment between the connectingstructure (600 from FIG. 6) and the payload assembly 704.

Another alignment feature may be the lateral (horizontal) distance 718between the mating surfaces 706B and 7101B, which may be zero, as shownin FIG. 7. In one configuration, the mating surfaces 706B, 710B may becollinear. Thus, the mating surface 706B forms a straight line with themating surface 710B. Each vertical mating surface 706B, 710B may set alateral position reference between the attachment points 602, 606. Thisprecisely specifies the location of the payload assembly 704 relative tothe base assembly 702 in the horizontal direction (DOF 618 in FIG. 6) atthe point of attachment between the connecting structure (600 in FIG. 6)and the payload assembly 704.

Another alignment feature may be a pair of collinear line segments (thatare also mating surfaces) 708A, 708E that interface the base side 702,are remote from point 714 and are collinear with 706A, 706E. The linesegments 708A, 708E constrain the rotation of the planar object 600about a normal to the plane of FIG. 7. Note that attachment point 604could also interface to the payload side 704, and the constraint wouldbe identical. This rotational constraint may completely restrain theconnecting element 600 in the desired DOFs. Otherwise, rotation in-planeof FIG. 7 would nullify the proper function of the vertical andhorizontal position reference features described above.

In summary, the base and payload planes in FIG. 7 are parallel andseparated by a specific distance 712. In this example, the sets ofcollinear line segments 706A, 706E, 710A, 710E that define theseparation distance are also parallel, and the lateral positionreference 718 is zero (collinear line segments 706B, 710B) between thetwo connected objects 702, 704.

Thus, the connecting element 600 in FIG. 6 not only supports a payload704 relative to a base 702 in 2 DOFs 618, 620, but also preciselylocates the payload 704 relative to a base 702 in these same DOFs.Hence, three of these structures 600 would not only provide kinematicattachment between a payload and a base, but also completely andprecisely specify the location and orientation of the payload relativeto the base.

The method of engaging attachment points 602, 604, 606 may be the samefor the attachment portion 506 of the pseudo-kinematic connectingelement 500 shown in FIG. 5 and described above.

The above described connecting structure also applies for the moregeneral case of non-parallel base and payload plates.

Design/Fabrication Considerations

Since the alignment features of the connecting element 600 discussedabove are all coplanar lines, a mask with the desired pattern can bemade for the patterning process (e.g., lithography). The patterningprocess can locate alignment features with high precision in a substratewafer plane immediately adjacent to the mask.

In some applications, it may be important to consider two design andfabrication points for connecting elements 500 (FIG. 5) and 600 (FIGS. 6and 7). First, the mask sides or regions of a substrate wafer intendedto form mating features should be substantially in contact with the masksides of other elements for highest precision. For example, for highestprecision, the mask sides in FIG. 7 should be the upper surface of thebase assembly 702 and the lower surface of the payload assembly 704.

Second, a micromachining process may either etch (cut) through thesubstrate wafer in a perfectly perpendicular manner or with a draft(e.g., inward draft). Etching the substrate in a perfectly perpendicularmanner is the ideal case. If drafting occurs, it is recommended to havean inward draft with acute angles measured from the mask plane to theetched sides of the substrate wafer. It may be important to ensurecontact at the masked side of the substrate wafer. In one embodiment,the amount of draft should be as small as practical, such as just enoughdraft to ensure there is nothing beyond a perpendicular cut (outwarddraft; obtuse angle) within the error of the micromachining process. Forexample, in one configuration, the draft is half a degree.

As a result of inward drafts, some of the ideal line contacts, shown inFIG. 7 as mating surfaces 706B, 706D, 708B, 708D, 710B, and 710D, may bereduced to point contacts with very shallow angles. The mating surfaces706A-E, 708A-E, and 710A-E for the base assembly 702, the payloadassembly 704 and the connecting element 600 may all experience drafts.Thus, the mating surfaces 706B and 710B (which define lateral positionreference line segments 718) may actually be contact points on the masksides of the base assembly 704 and the payload assembly 706. Inwarddrafting may be acceptable because the two planes of two matingsurfaces, which coincide at a point contact, form a very acute angle.Thus, if a load is applied, a substantial contact patch may be formed,and hence result in reasonable contact stresses.

Internal Load and Flexure Assembly

To obtain maximum accuracy, the mating features described herein may bepreloaded together with an externally-applied load (e.g., to seat matingfeatures during a bonding operation) or an internally-reacted set ofloads. In the latter case, the preload may be permanently applied andbonding may not be necessary. Internally reacted loads may be created bydeflecting a flexure assembly (see FIG. 8) that is micromachined intoone or more of the connected planar structures.

FIG. 8 is a side view of one embodiment of an internal flexure assembly800 (also referred to herein as an “internal preloader” or “preload”).The internal flexure assembly 800 comprises a set ofdouble-parallel-motion flexures 802A-802B, 804A-802B(double-parallel-motion set) with outer ends connected to a wafer 806.In one embodiment, the internal flexure assembly 800 may furthercomprise a preloader stage 808 connected to the inner ends of theflexures 802A-802B and 804A-802B. The stage 808 constitutes a linearmotion control device and hence may be called a “stage.” In oneembodiment, it is desirable to have a hole 810 on at least one side ofthe preloader stage 808 for inserting a preloader pin (see FIG. 10).

In some applications, it is desirable to use the internal flexureassembly 800 to provide internal preloading in a substrate wafer,thereby seating mating surfaces together without a deadband. Internalpreloading occurs when the flexures 802A-802B, 804A-804B are deflectedby the action of inserting a preloader pin, or more generally a matingfeature of another planar structure.

Each flexure 802A-802B and 804A-804B constrains DOFs such that thepreloader stage 808 is supported very stiffly in five DOFs, but is softin the one remaining DOF 812 (i.e., forming a spring). This soft DOF 812is in the direction where the preload is applied. An applied deflection816 results from a force 814 applied at the preloader stage 808. Theforce 818 is equal to and opposite to a resultant force 814 (internallyreacted force) applied by the preloader stage 808 to the connected wafer806 in the vertical direction in FIG. 8. The force 818 is the preloadforce used to positively seat a mating element against referencefeatures (see FIGS. 9 and 11). In one embodiment, a relatively largedeflection 816 is required to generate a preload 818.

The internal flexure assembly 800 in the planar structure of FIG. 8 maybe micromachined with high accuracy. Thus, the flexures 802A-802B,804A-802B may have highly-accurate stiffnesses. Thus, deflections 816 ofthe flexures 802A-802B, 804A-802B should generate very accurate,repeatable and/or predictable preloads from device to device. Byinternally reacting these accurately-defined preloads, negligibledistortion may occur in mated structures.

A maximum deflection capability defined by a “deflection stop” 820 maybe implemented to limit the motion of the preloader stage 808. If theapplied deflection 816 is close to the deflection stop 820, then motionsof an assembled structure (because of further elastic deflection of thepreloader stage 808 due to inertial or external loads on the assembly)will be limited to the difference in height 822 between the applieddeflection 816 and the maximum deflection 820.

Tab and Slot

In some configurations, it is desirable to attach micromachined passivealignment assemblies using male and female connectors, such as by way ofexample, a tab and slot attachment scheme.

FIG. 9 illustrates two examples of preloading using a tab and slotattachment scheme with the internal flexure assembly 800 of FIG. 8. Thetab 902 may be used as an attachment point for a connecting element, ora male or female connector for a base or payload assembly. The tab 902has two substantially vertical mating surfaces 904 and 906, and twohorizontal mating surfaces 908 and 910.

In FIG. 9, a connecting object 912 (such as a horizontal wafer) has anopening or slot for inserting the tab 902 (FIG. 9 is a section viewalong the long axis of the slot, normal to the plane of object 912, andin the plane of the tab 902). The connecting object 912 may have matingsurfaces such as surfaces 914, 916 that serve as counterparts to themating surfaces 904, 906 of the tab 902. When the tab 902 is insertedinto the slot, the vertical mating surfaces 904, 906 (horizontalconstraint features) of the tab 902 rest against the ends 914, 916 ofthe slot in the connecting object 912, and the horizontal matingsurfaces 908, 910 (vertical constraint features) of tab 902 rest againstthe lower surface of object 912.

In one example of preloading, if a lateral position/motion constraint isdesired, one substantially vertical mating surface 904 of the tab 902 ismade to bear against one end 914 of the slot. The other end 916 of theslot comprises a stage for a flexure preloader 934. The substantiallyvertical mating surface 906 of the tab 902 may be formed at an angle 918(angle relief) to enable initial vertical engagement against the end 916of the slot. When the tab 902 is fully seated in the vertical directionin the slot of the connecting object 912, the preloader stage 934 isdisplaced laterally (to the left, as indicated by an arrow 920) asufficient amount to generate a desired load 922 (to the right) againstthe mating surface 906 of the tab 902.

Another example of preloading in FIG. 9 involves the internal flexureassembly 924 (also called a flexure preloader) in the tab 902 as avertical position/motion constraint. The internal flexure assembly 924is micromachined into the tab 902 with a soft DOF 926 of the preloaderstage 928 in the vertical direction. When the tab 902 is approximatelyseated vertically (i.e. surfaces 908 and 910 in approximate contact withconnecting object 912), there is a hole 930 whose top edge is thepreloader stage 928 and whose bottom edge and sides are in the tab 902.

In one embodiment, the bottom edge of the hole 930 is a horizontalsurface of a part 932 of the connecting object 912 (wafer). The shape ofthe hole 930 may be rectangular, circular, polygon or other shape,depending on the design of the micromachined passive alignment assembly.A separate structure called a preloader pin (see FIG. 10) may beinserted in the hole 930 in FIG. 9 to generate a vertical preload forcepair 936, 938 (via upward displacement of the stage 928). The force 936acts on the tab 902 and force 938 acts on the part 932 of connectingobject 912 that forms the bottom of hole 930. These forces 936, 938 arethen reacted across the horizontal mating surfaces 908, 910 and thelower surface of object 912 by force pairs 940, 942 and 944, 946, whichforces these surfaces into intimate contact and creates a more precise(i.e. deadband free) vertical position constraint. At this point, in theabsence of any flexured “ball joint” type structure attached to tabelement 902, a vertical constraint on the paired surfaces 908 and 910also creates a (possibly redundant) rotational constraint out of theplane of FIG. 9. This may be acceptable (see sections “RedundantElements for Additional Stiffness / Planarity Enforcement” and “OpticalElement Support Structure”).

FIG. 10 is a three-dimensional view of one embodiment of a preloader pin1000. The preloader pin 1000 may be fabricated using patterning andmicromachining processes discussed herein. The preloader pin 1000 may bemade of silicon, plastic or some other suitable substance. Thecross-section of the preloader pin 1000 may be a rectangle, a circle, asquare, a polygon or some other suitable shape. In one embodiment, theend of the preloader pin 1000 has a substantially square cross-sectionwith four sides that are preferably about 500 microns in length. Theshape of the right cross-section end of the preloader pin 1000 isconfigurable and may depend on the shape of the hole 930 in FIG. 9, suchthat when the preloader pin 1000 is fully inserted in the hole 930, thepreloader stage 928 is deflected vertically a desired amount.

Gently tapering the preloader pin 1000 in the vertical direction 1002allows a low-force initial insertion and engagement. In someapplications, the preloader pin 1000 is maintained in the hole 930 (FIG.9) by friction. The frictional holding should be good to several hundredtimes gravitational acceleration. In other applications, it may bedesirable to dispense an adhesive (e.g., spot of glue) on the preloaderpin 1000 to restrain the pin 1000 in the hole 930.

In FIG. 10, the preloader pin 1000 may comprise a stop flange 1004 toprovide a positive stop location after inserting the preloader pin 1000in the direction of insertion 1008. The preloader pin 1000 may alsocomprise an edge relief 1006 to allow for any sharp corners of themating surfaces in the preloader stage 928 (FIG. 9) or hole 930.

In FIG. 9, the flexure preloader 934 and the other flexure preloader(internal flexure assembly 924) each form an internally-reacted set ofloads. In the first example described above, the force reaction pointsare the two substantially vertical mating surfaces 904 and 906 of thetab 902 and the two ends 914 and 916 of the slot, where one end 916comprises a stage of a flexure preloader 934. The preload 920 causessimple compressive stress locally in the tab 902, and a somewhat morecomplex yet still local tensile stress pattern around the slot. Byvirtue of the softness of the preloader 934, the forces and hencestresses can be made very small in absolute value. Since strain isproportional to stress, and overall distortion is proportional to straintimes a distance, small localized strains create negligible overalldistortions.

FIG. 11 illustrates an assembly 1100 where two internal flexureassemblies 1102 and 1104 are used to maintain the 2-DOF, in-planeposition of a tab 1106, i.e., maintain contact at mating surfaces of aslot. The tab 1106 in FIG. 11 may represent a top view of the tab 902 inFIG. 9, and a planar object 1100 in FIG. 11 may represent a top view ofthe connecting object 912 in FIG. 9. As in FIG. 9, the tab 1106 in FIG.11 fits in a slot in the object 1100. Thus, an internal flexure assembly1102 in FIG. 11 may represent the flexure preloader 934 described abovein the first preloading example of FIG. 9. The internal flexure assembly1102 in FIG. 11 controls the vertical position of the tab 1106 in FIG.11 by preloading surface 1118 of tab 1106 against surface 1120 of planarobject 1100. These surfaces are analogous to 904 and 914, respectively,in FIG. 9.

The other internal flexure assembly 1104 in FIG. 11 controls thehorizontal position of the tab 1106. The internal flexure assembly 1104has a hole 1108 configure to receive a preloader pin 1110. FIG. 11 showsan end view of the preloader pin 1000 in FIG. 10. When a preloader pin1110 is inserted into the hole 1108, the pin 1110 causes a horizontaldeflection 1112 (to the right) of a preloader stage 1114, which causes ahorizontal force 1116 (substantially equal and opposite to thedeflection 1112) applied by the preloader stage 1114 on the pin 1110 andthe tab 1106. This forces surface 1122 of tab 1106 into intimate contactwith surface 1124 of planar object 1100.

Partially-Degenerate, Partially-Redundant, Pseudo-Kinematic Designs

The level of stiffness or softness of a particular DOF depends on designfactors such as plate stiffness of an attached structure, a desiredprecision of position, thermal and dynamic environment, etc. Analignment assembly may be designed to be partially-degenerate,partially-redundant or a pseudo-kinematic design with substantially sixstiff DOFs.

To construct a partially-degenerate support, design analysis determinesresonant modeshapes and frequencies and verifies that the modeshapes andfrequencies do not negatively impact the design.

For a partially redundant support, an appropriate analysis involvesapplication of dynamic and thermal environments to verify thatdistortions caused by the dynamic and thermal environments are less thanthe desired precision.

For many applications of these micromachined pseudo-kinematicstructures, there may be two things in common: (1) all componentstructures may be made of silicon and (2) the payload and the base maybe parallel. Where either of these conditions occur, it is possible togreatly relax the constraints of kinematicity. If a structure is allsilicon, a highly redundant support system can be used. If redundantDOFs are properly chosen, the payload may only experience warping in thepresence of high thermal gradients, which is unlikely given the highconductivity of silicon and the small dimensions involved. If asymmetric support is used and the base and payload are parallel, bulktemperature changes would cause only a piston shift (no lateral, tip,tilt, or roll shift).

The design and fabrication combination of solid modeling software andlithographic micromachining allows the construction of multi-partassemblies where the fit-up on assembly may be virtually perfect, evenwith complex geometries. The construction of multi-part assemblies wherethe fit-up on assembly may be virtually perfect may obviate the need forkinematic attachment in many cases. In the macroscopic world, much ofthe need for kinematic support is due to imperfections of the mountingsurfaces.

An added benefit of a redundant support is greater stiffness of each ofthe component parts of the assembly. Extended line contacts effectivelyrestrain out-of-plane deformations in a wafer.

Fiber Termination Array Assembly

FIG. 12A is a three-dimensional enlarged view of one embodiment of afiber termination array assembly 1200 (also called a fiber alignmentdevice). FIG. 12B is a three-dimensional assembled view of the fibertermination array assembly 1200 in FIG. 12A. The fiber termination arrayassembly 1200 may be formed by one or more processes described inco-assigned U.S. patent application Ser. No. 09/855,305, entitled“ANGLED FIBER TERMINATION AND METHODS OF MAKING THE SAME”, which ishereby incorporated by reference in its entirety. The fiber terminationarray assembly 1200 comprises a fiber locator plate 1202, a fibertermination plate 1204 and three connecting elements 1206A-1206C.

The fiber termination plate 1204 has a polished optical surface 1216,holes 1220 configured to support/align optical fiber ends and kinematicpositioning slots 1208, 1214 (with mating surfaces). The slots 1208,1214 are configured to receive a tab (with mating surfaces), such as tab1210, of the connecting elements 1206A-1206C. The fiber locator plate1202 also has holes 1218 configured to support/align optical fibers andslots, such as slot 1212, configured to receive a tab of the connectingelements 1206A-1206C. In one configuration, the connecting elementprotrusions 1222 form extended line contacts that effectively restrainout-of-plane deformations in the fiber termination plate 1204 and/or thefiber locator plate 1202.

The three connecting elements 1206A-1206C constrain the fibertermination plate 1204 to the fiber locator plate 1206 with about sixDOFs. Each connecting element 1206 may control two DOFs of position andmay have four to five DOFs of stiffness. Although one connecting element1206A may be redundant in a stiffness DOF in view of the otherconnecting elements 1206B, 1206C, each connecting element controls twoDOFs of position and may precisely position the fiber locator plate 1202with respect to the fiber termination plate 1204.

In some applications, it may be desirable to connect the fibertermination plate 1204 and the fiber locator plate 1202 with more thansix stiff DOFs. For example, more than six stiff DOFs are used toreinforce flatness, add stiffness, and prevent sagging under gravity orvibration for the fiber termination plate 1204 and the fiber locatorplate 1202.

In one embodiment, the assembly 1200 was analyzed for polishing pressureon an optical face on the fiber termination plate 1204 and found to havedeformations on the nanometer level with typical polishing pressures.

As shown in FIGS. 12A and 12B, two objects, such as two planar siliconwafers, may be positioned precisely relative to each other in six DOFs(tip, tilt, piston, roll, and two in-plane DOFs (lateral to separationdirection)) to lithographic levels of precision or exactness. The twoobjects may be positioned by using planar connecting structures, eachwith mating reference features to control one or more DOFs between thetwo objects for a total of six DOFs. The objects and connectingstructures may all be fabricated using lithographic micromachiningtechniques, or their equivalents in precision. The two objects to bealigned may contain arrays of optical components, which are alreadyprecisely positioned within the plane such that the two arrays would beprecisely positioned relative to each other.

If the above positioning concept has no internal preloading, some gapsare allowed between mating features to ensure assembly. These gaps maycontribute to the overall error in the positions of objects in theassembly.

If the above positioning concept has internal preloading, internallyreacted loads ensure contact between mating surfaces, remove any gapsand allow a very high assembly precision.

Redundant Elements for Additional Stiffness / Planarity Enforcement

Large pseudo-kinematically supported planar arrays may be designed withextra bending stiffness to resist inertial loads. To implement extrabending stiffness, redundantly-attached ribs may be added to a mainwafer plane. The redundantly attached ribs may be designed to actuallyenforce the flatness of the main wafer. This enforcement may be done tolithographic precision.

FIG. 13 is a side view of two embodiments of redundant connectingelements 1302 (also called ribs) and 1304 and a plate 1306 (also calledwafer). The wafer 1306 may be used as an optical bench to supportoptical elements 1308, 1309 such as fibers, lenses or mirrors. In oneembodiment, a wafer 1306 (e.g., a base assembly or a payload assembly)is supported with more than six stiff DOFs to enforce flatness (i.e.,planar surface control), add extra stiffness, resist inertial loads(e.g., sagging or bending under gravity or vibration of the wafer 1306),and/or resist externally-applied loads from the environment. Thus, lessstrains or distortions are communicated to the optical elements 1308 andtheir positions remain more precise.

The connecting elements 1302 and 1304 may be designed with redundanttabs 1310A-1310C, 1314A-1314C (also called attachment points). Theconnecting elements 1302 and 1304 may be fabricated with high precisionusing the patterning and micromachining processes discussed above.

In one embodiment, the connecting element 1302 has tabs 1310A-1310C thatmay engage into slots 1312A-1312C of the wafer 1306. The attachmentmechanism of the tabs 1310A-1310C and slots 1312A-1312C may encompassexternal preloading and gluing of the tab into the slot. FIG. 13 shows atab 1320 of a connecting element, such as connecting element 1302, thatis flush with the top surface of the wafer 1306.

In another embodiment, the connecting element 1304 has tabs 1314A-1314Cwith internal flexure assemblies 1316 (with preloaders), which aremicromachined in the tabs 1314A-1314C. The attachment mechanism of thetabs 1314A-1314C and slots 1312A-1312C may follow the second exampledescribed above with reference to FIG 9. FIG. 13 shows a tab 1318 of aconnecting element, such as connecting element 1304, protruding from atop surface of the wafer 1306. Each tab 1318 may use a connecting pin(not shown).

FIG. 14 is a three-dimensional view of the two connecting elements 1302and 1304 and the plate 1306 of FIG. 13. FIG. 14 shows protruding,attached tabs 1318A, 1318B and attached tabs 1320 that are flush withthe top surface of the wafer 1306. The tabs 1318A, 1318B, 1320 are partof connecting elements underneath the plate 1306. Each connectingelement 1302, 1304 may have any number of tabs, such as six tabs, asshown in FIG. 14.

Pseudo-Kinematic vs. Partially-Degenerate Support

FIGS. 15, 16 and 17 illustrate the difference between a pseudo-kinematicsupport system and partially-degenerate support systems. FIG. 15 is athree-dimensional view of one embodiment of a pseudo-kinematic supportsystem 1500. The pseudo-kinematic support system 1500 in FIG. 15comprises a box-like structure 1510 and three pseudo-kinematic, planar,bipod connecting elements 1502A-502C (referred to as “bipod connectingelements”). Each bipod connecting element 1502 may have two stiff orvery stiff DOFs. For example, bipod connecting element 1502A has twostiff DOFs 1504A-1504B. Bipod connecting element 1502B has two stiffDOFs 1506A-1506B. Bipod connecting element 1502C has two stiff DOFs1508A-1508B. Thus, the bipod connecting elements 1502A-1502C mayconstitute a complete support (six stiff DOFs) for the box-likestructure 1510 (e.g., base assembly or payload assembly). The remainingDOFs (not shown in FIG. 15) may be soft. To determine whether or not aset of support DOFs is kinematic, redundant, or degenerate, thedirections and points of application of each set of support DOFs shouldbe considered. Kinematic may also be referred to as “determinate” or“statistically determinate.” Redundant may also be referred to as“indeterminate” or “statistically indeterminate.”

In some applications, it is desirable to have a degenerate supportsystem, for example, when building a motion control stage. A degeneratesupport system constrains base and payload assemblies with less than sixDOFs. As a result, there may be some trajectory (i.e. combination ofCartesian DOFs) of the payload assembly relative to the base assemblythat is unconstrained. A degenerate support system may occur when aconnecting element is missing or when certain connecting elements areparallel.

Although a degenerate support and a partially-degenerate supportconstrain base and payload assemblies with less than six DOFs, adegenerate support will move in some trajectory direction that isunconstrained while a partially-degenerate support will move in sometrajectory direction that is resisted by soft DOF(s) from thepseudo-kinematic connecting elements. The trajectory direction of thedegenerate support would have no restoring force and zero resonantfrequency. Meanwhile, the trajectory direction of thepartially-degenerate support would have relatively little restoringforce, and a relatively low resonant frequency.

FIG. 16 is a three-dimensional view of one embodiment of apartially-degenerate support system 1600. The partially-degeneratesupport system 1600 in FIG. 16 comprises a box-like structure 1612, twopseudo-kinematic, planar, bipod connecting elements 1602A-1602B(referred to as “bipod connecting elements”) and one pseudo-kinematic,planar, monopod connecting element 1604 (referred to as “monopodconnecting element”). While the two bipod connecting elements1602A-1602B each have two stiff DOFs 1606A-1606B, 1608A-1608B, themonopod connecting element 1604 has one stiff DOF 1610. Because thebipod connecting elements 1602A-1602B and the monopod connecting element1604 are pseudo-kinematic, the remaining DOFs (not shown) may be soft.

Since the partially-degenerate support system 1600 restrains thestructure 1612 with five stiff DOFs 1606A-1606B, 1608A-1608B, and 1610,there may be some trajectory direction 1614 for the structure 1612.Motion in this trajectory (motion direction) 1614 is resisted byout-of-plane bending of the bipod connecting elements 1602A-1602B andin-plane or out-of-plane bending of the monopod connecting element 1604,which are all fairly soft DOFs. Motion along trajectory direction 1614would therefore have little restoring force, and thus would have a lowresonant frequency. The compliance in trajectory direction 1614 wouldalso mean any precise positioning features designed to control motionalong the trajectory direction 1614 may have degraded performance.

FIG. 17 is a three-dimensional view of another embodiment of apartially-degenerate support system 1700. The partially-degeneratesupport system 1700 comprises three connecting plates 1710A-1710C andthree pseudo-kinematic, planar, bipod connecting elements 1702A-1702C(referred to as “bipod connecting elements 702A-1702C”). Each bipodconnecting element 1702A-1702C has two stiff or very stiff DOFs. Forexample, bipod connecting element 1702A has two stiff DOFs 704A-1704B.Bipod connecting element 1702B has two stiff DOF 1706A-1706B. Bipodconnecting element 1702C has two stiff DOF 1708A-1708B.

In one embodiment, where the three plates 1710A-1710C are rigidlyattached to each other, the system 1700 has a total of six stiff DOFs1704A-1704B, 1706A-1706B, 1708A-1708B. The remaining DOFs (not shown)may be soft.

Because the attachment points of the three bipod connecting elements1702A-1702C are collinear, one bipod connecting element 1702A may beineffective. Thus, the three connecting plates 1710A-1710C with threebipod connecting elements 1702-1702C may have only four stiff DOFs,including two trajectory directions 1712 and 1714 with very lowstiffness.

Strain Isolation

As explained above, one or more internal flexure assemblies may seatmating surfaces together without a deadband. One or more internalflexure assemblies may also be used to resist load-induced ortemperature-induced strains/distortions in a base assembly fromtransferring to a payload assembly, or vice versa. At most, there may bea position shift and/or an attitude shift of the base assembly withrespect to a payload assembly, or vice versa.

FIG. 18 is a three-dimensional view of one embodiment of a strainisolation flexure assembly 1800. The strain isolation flexure assembly1800 in FIG. 18 comprises one or more payload assemblies 1810 and a baseassembly 1808 with micromachined features, such as three micromachinedouter internal flexure assemblies 1802A-1802C (i.e., “strain-isolationmounting flexures” or “mounting flexures”), a plurality of holes 1814and a set of inner internal flexure assemblies 1816A-1816C around eachhole 1814.

The outer internal flexure assemblies 1802A-1802C in FIG. 18 may beoriented 120 degrees apart, as shown in FIG. 18, or oriented at anyarbitrary angle or distance from each other, preferably with thelines-of-action 1804A-1804C (i.e., soft direction of the flexure system)meeting at some common point, such as point 1806. In some applications,it may be desirable to have less than three or more than three outerinternal flexure assemblies in the strain isolation flexure assembly1800.

Each outer internal flexure assembly 1802 controls two DOFs, such as DOF1818A (vertical, out-of-plane) and DOF 1818B (in-plane). FIG. 18illustrates three lines of action 1804A-1804C that intersect at acentroid 1806. The three lines of action 1804A-1804C represent degreesof flexibility or soft DOFs provided by the outer internal flexureassemblies 1802A-1802C.

Any distortion or strain in a foundation (not shown), to which the baseassembly 1808 is attached via flexure assemblies 1802A-1802C, can beaccommodated by motion along the lines of action, thereby generatingonly minute forces in the base assembly 1808 from restoring forces inthe flexure systems 1802A-1802C. Thus, the outer internal flexureassemblies 1802A-1802C may prevent load-induced strains/distortions in afoundation from communicating to the base assembly to 1808, and hencemaintain the relative location of one or more payload assemblies 1810,which are attached to the base assembly 1808. Thus, the flexureassemblies 1802-180C may be called “strain isolation mounting flexures.”At most, there may be a position shift and/or an attitude shift of thebase assembly 1808 with respect to the foundation, or vice versa.

The outer internal flexure assemblies 1802A-1802C maintain apseudo-kinematic state between the base assembly 1808 and thefoundation. The pseudo-kinematic state may be particularly importantwhen the base assembly 1808 is used as an optical bench to supportpayload assemblies 1810. Maintaining a pseudo-kinematic state betweenthe base assembly 1808 and the foundation reduces the amount ofstrains/distortions in the base assembly 1808, hence maintaining therelative positions of the payload assemblies 1810.

Thermal Compensation

FIG. 19 illustrates a part of the base assembly 1808 in FIG. 18, apayload assembly 1810, an optical element 1812 supported by the payloadassembly 1810, an outer internal flexure assembly 1802, a hole 1814 anda set of inner internal flexure assemblies 1816A-1816C around the hole1814. One or more optical elements 1812 may be inserted in each hole1814. The payload assembly 1810 (e.g., silicon optical bench) in FIG. 19is directly connected to the base assembly 1808, and the connectionpoints are flexured to attain a pseudo-kinematic state.

In other embodiments, there may be more than three or less than threeinner internal flexure assemblies 1816A-1816C. The inner internalflexure assemblies 1816A-1816C may be oriented 120 degrees apart ororiented at any arbitrary angle or distance or angle from each other,preferably with the lines-of-action 1908A-1908C meeting at a commonpoint (e.g.1910). For example, the inner internal flexure assemblies1816A-1816C in FIG. 19 are oriented 90 degrees apart.

The inner internal flexure assemblies 1816A-1816C in FIG. 19 may bereferred to as thermal compensation flexures, which may be used tomaintain hot die passive alignment. The inner internal flexureassemblies 1816A-1816C together may be called a thermal compensationflexure assembly.

FIG. 19 illustrates three lines of action 1908A-1908C that intersect ata centroid 1910. The three lines of action 1908A-1908C represent degreesof flexibility or soft DOFs provided by the inner internal flexureassemblies 1816A-1816C. An optical element 1812, such as a diode, willexpand as the element 1812 rises in temperature (generates or absorbsheat). Thus, the optical element 1812 and its payload assembly 1810 willattempt to increase in size relative to the payload assembly'sattachment points to the base assembly 1808. Because the inner internalflexure assemblies 1816A-1816C allow for or compensatetemperature-induced distortions along the lines of action 1908A-1908C,the expanding optical element 1812 and its payload assembly 1810 willnot cause any warping or stresses to the base assembly 1808. The opticalelement 1812 and the payload assembly 1810 will be at substantially thesame temperature and hence will generate no internal stresses ordistortions (other than simple expansion).

The inner internal flexure assemblies 1816A-1816C also maintain thecenter of the expanding payload assembly 1810 (and optical element 1812)at the centroid 1910 of the flexure systems lines-of-action. In someapplications, maintaining centration of the expanding optical element1812 is critical. For example, an incident laser beam may be required toremain at a certain spatial position on a diode. The spatial positionfor instance, is the center of the diode. With a thermal compensationflexure assembly in FIG. 19, the laser beam will remain at its spatialposition even when the diode expands or contracts. If the diode expandsor contracts, the neutral point is the center of the diode, and thecenter of the diode will not move spatially laterally, relative to thebase assembly 1808.

Chuck Array

FIG. 20 is a three-dimensional view of one embodiment of a micromachinedalignment assembly 2000, which comprises a base assembly 2006 and apayload assembly 2004 (also called “chuck arrays” or “wafers” or “planarobjects”). In another embodiment the top structure 2004 may be the base,and the bottom structure 2006 may be the payload. The micromachinedalignment assembly 2000 in FIG. 20 may constitute a view of one-third ofa two-piece, ring-shaped alignment assembly. The base assembly 2006 andpayload assembly 2004 each comprise an array of micromachined chucks orholes 2002 for restraining and aligning arrays of optical elements 2008,such as mounted lenses, fibers, or mirrors. The chucks 2002 may beformed by one or more processes described in the above-referenced U.S.Patent Application, entitled “OPTICAL ELEMENT SUPPORT STRUCTURE ANDMETHODS OF USING AND MAKING THE SAME” Ser. No. 10/001092, which ishereby incorporated by reference in its entirety.

FIG. 21 is an enlarged three-dimensional view 2100 of one part of themicromachined alignment assembly 2000 (“chuck array”) in FIG. 20. FIG.21 illustrates a bipod-style connecting element 2108 (e.g., a planarstructure) with two tabs 2102A-2102B for pseudo-kinematic (lowdistortion) or redundant (planarity enforcing) attachment of the baseassembly 2006 and the payload assembly 2004. An alignment assembly maycomprise two ring-shaped structures, which are partially shown in FIGS.20 and 21, and a plurality of bipod-style connecting elements (e.g.,three), such as the bipod-style connecting element 2108 in FIG. 21.

In one embodiment, each connecting tab 2102A, 2102B in FIG. 21 is aplanar structure with two stiff DOFs. DOFs 2110, 2112, 2114 arecontrolled at the payload assembly 2004. DOFs 2110, 2114 are used by thepayload assembly 2004, and DOF 2112 is used by the connector tab 2102A.DOFs 2116, 2118 are redundant, which may or may not be used. DOF 2116may be used by the payload assembly 2004 to enforce planarity, and DOF2118 may be used by the connecting structure 2108 to enforce planarity.

With three bipod-style connecting elements, such as the bipod-styleconnecting element 2108 in FIG. 21, the payload assembly 2004 and thebase assembly 2006 may be supported by a total of six stiff DOFs. Theconnector tabs 2102A-2102B have internal flexure assemblies 2104A, 2104Bthat provide compliance in the vertical direction for preloader stages2106A, 2106B, which in turn may be used (with a preloader pin, notshown) to provide preload to controlled DOFs 2110 and 2116. Similar tothe vertical preload example of FIG. 9, a possibly redundant rotationalconstraint normal to the plane of connecting structure 2108 may also becreated. The micromachined alignment assembly 2000 shown in FIGS. 20 and21 may accurately control the lateral positions of the payload assembly2004 with respect to the base assembly 2006, and thus control thelateral positions (desired orientation) of upper and lower portions ofthe optical elements 2008.

In one embodiment, each bipod-style connecting element 2108 utilizesneighboring flexure systems in the base and payload wafers 2006, 2004 toprovide preloading for the other DOFs indicated in FIG. 21. For example,a first connecting tab 2102A of the bipod-style connecting element 2108in FIG. 21 has neighboring flexure systems 2120A and 2120B. FIG. 11shows a top view of a connecting tab 1106 that may represent connectingtab 2102A in FIG. 21. The two flexure systems 2120A and 2120B, togetherwith their respective preloader stages and preloader pins (not shown)allow for application of preload to control DOFs 2112 and 2114. Flexuresystems 2120C, 2120D provide similar capability at the attachment of2108 to the base assembly 2006.

The connecting structures between two objects (e.g., a base and apayload) disclosed herein may be pseudo-kinematically supported, whichallows the connecting structures to be used for precision positioningand distortion free support of optical components.

Optical Element Support Structure

FIG. 22 is a three-dimensional view of one embodiment of an assembly2200, which comprises a first structure 2210 (e.g., a base assembly or apayload assembly), a plurality of connecting elements 2202A-2202C and asecond structure 2208 (e.g., a base assembly, a payload assembly or anoptical element, such as a mirror). In one configuration, the assembly2200 may be an all-silicon fold mirror.

Other embodiments of the assembly 2200 may have less than three or morethan three connecting elements. The connecting elements 2202A-2202C haveredundant attachment points 2204A-2204F on one end and pseudo-kinematicattachment points 2206A-2206C on the other end. The six redundantattachment points 2204A-2204F may connect to the first structure 2210.The three pseudo-kinematic attachment points 2206A-2206C may connect tothe second structure 2208.

Other embodiments of the connecting elements 2202A-2202C may have lessor more attachment points.

FIG. 23 is an enlarged view of a redundant attachment point 2204A of oneconnecting element 2202A in FIG. 22. The redundant attachment points2204A-2204F of the connecting elements 2202A-2202C in FIG. 22 attach tothe base assembly 2210 collectively with more than six stiff DOFs. InFIG. 23, the redundant attachment point 2204A is connected to the baseassembly 2210 with two possibly stiff DOFs 2302A-2302B, in addition tothe DOFs (e.g., three translations) used for pseudo-kinematicattachment. Similarly, the redundant attachment points 2204B-2204F areeach connected to the base assembly 2210 with two additional possiblystiff DOFs (not shown). Therefore, the three connecting elements2202A-2202C attach to the base assembly 2210 with twelve additionalpossibly stiff DOFs.

In some applications, other designs for the connecting elements may beused to attach the base assembly in more than six DOFs. For example, aconnecting element may have three redundant attachment points. Therationale for allowing these redundant DOFs in this assembly is the sameas discussed in the section “Redundant Elements for AdditionalStiffness/Planarity Enforcement” (e.g., enforcing the planarity of thebase and/or connecting elements).

FIG. 24 is an enlarged view of a pseudo-kinematic attachment point 2206A(also called mounting tab) of one connecting element 2202A in FIG. 22.The attachment point 2206A in FIG. 24 may embody some or all of theprinciples of kinematic support and position control described above.The pseudo-kinematic attachment points 2206A-2206C of the connectingelements 2202A-2202C in FIG. 22 attach to the optical element 2208collectively with six stiff DOFs. FIG. 24 illustrates onepseudo-kinematic attachment point 2206A with two stiff DOFs 2402A,2402B. Similarly, the other pseudo-kinematic attachment points 2206B,2206C are connected to the optical element 2208, each with two stiffDOFs (not shown).

In one embodiment, each pseudo-kinematic attachment point 2206 has aflexure system 2408A and 2408B (FIG. 24) that is designed to provide anappropriate stiffness to form a ball joint with stiff DOFs 2402A, 2402B,2406. DOFs 2402A, 2402B pseudo-kinematically support the mirror wafer2208, and DOF 2406 is a constraint borrowed back from the opticalelement 2208 to support the end of the connecting element 2202A.

In one embodiment, the pseudo-kinematic attachment point 2206A usespositive preloaders (or preloading stage) to attach the connectingelement 2202A to the optical element 2208 without deadband, such thatDOFs 2402A, 2402B, 2406 are precisely specified and controlled (i.e.,possess high stiffness). In one configuration, the pseudo-kinematicattachment point 2206A uses three preloaders. One preloader 2412 appliesa preload against a surface of the pseudo-kinematic attachment point2206A using a preloader pin (not shown) to precisely specify and controlDOF 2406. Another preloader 2414 applies a preload against anothersurface (e.g., end of the tab in the slot) of the pseudo-kinematicattachment point 2206A without a pin (see FIGS. 9, 11) to preciselyspecify and control DOF 2402B.

A vertical preloader (not shown) in an upper portion of the attachmentpoint 2206A that protrudes above the optical element 2208 is similar tothe preloader stage 2304 in the redundant attachment point 2204A in FIG.23. The vertical preloader stage in the pseudo-kinematic attachmentpoint 2206A provides a preload in DOF 2402A. The vertical preloaderstage uses a preloader pin.

The flexure system 2405 has two flexure elements 2408A-2408B that form abipod-like structure. The two flexure elements 2408A-2408B intersect ata virtual point in the pseudo-kinematic attachment point 2206A and henceform a “ball joint” as previously described.

In one embodiment, the flexure system 2405 in FIG. 24 is recessed usingan extra micromachining step (an etch defined by the square area 2404),to decrease the depth 2410 of the flexure elements 2408A-2408B. Theflexure blade depth 2410 is then variable and not fixed as the thicknessof the wafer. Thus, flexure properties may be more readily tailored toachieve a desired pseudo-kinematic stiffness connectivity. For example,if the flexure elements 2408A-2408B are thinned sufficiently, they wouldbehave more like rods, and thus more perfectly constrain only two DOFs,i.e., have larger separation of stiffness between desired and undesiredconstraint DOFs.

The connecting elements 2202A-2202C in FIG. 22 may be fabricated usingthe manufacturing procedures described herein. For example, lithographyand micromachining can fabricate the connecting elements 2202A-2202Cwith high intrinsic precision. In one embodiment, a recessed flexuresystem (e.g., 2408A and 2408B in FIG. 24) in each connecting element2202 is formed by a patterning process, such as lithography, that formsa desired pattern, such as a rectangle, of the recessed flexure system2405 on one side of a substrate wafer. Then the rectangular area ispartially etched through the substrate wafer until a desired depth 2410for the flexure elements 2408A-2408B remains. The flexure system 2405could then be etched from the other side using an appropriate maskpattern to form the flexure elements 2408A-2408B.

In another embodiment, a patterning process such as lithography may beused to form a desired pattern of the flexure elements 2408A-2408B on asubstrate wafer. Next, a micromachining process such as an etchingprocess may be used to etch through the substrate wafer to apre-determined depth for thinning down the depth 2410 of the flexureelements 2406A-2406B. After the micromachining process, the substratewafer is cleansed. Next, the substrate wafer may be subjected to asecond patterning process. Then, the substrate wafer may be subjected toa second micromachining process to etch through the whole substratewafer. Finally, the substrate wafer is cleansed and then assembled toprovide the desired micromachined passive alignment assembly.

Megastack

FIG. 25 is a three-dimensional view of one embodiment of a megastackstructure 2500. The megastack structure comprises a base plate 2502 andone or more side plates 2504A, 2504B. The configuration with onesideplate 2504 may be referred to as an “L-type megastack,” and theconfiguration with two side plates 2504A, 2504B, shown in FIG. 25, maybe referred to herein as a “C-type megastack.” The megastack structure2500 enables precise dimensional support of an arbitrarily large numberof payload assemblies 2506, which may comprise silicon wafers with MEMsdevices or integral or mounted optical devices. Optical elements 2508may be mounted, restrained, and/or aligned on a payload assembly 2506.In some applications, a side plate 2504 may also serve as a payloadassembly that mounts, restrains, and/or aligns optical elements.

As shown in FIG. 25, the megastack structure 2500 has precisely-formedattachment points 2510A-2510C (also called “slots”) to support and aligneach payload assembly 2506. Each attachment point 2510 provides two-DOFpositioning control in the C type megastack configuration to attain apseudo-kinematic support condition.

The side plates 2504A-2504B may or may not be kinematically attached tothe base plate 2502. As shown in FIG. 25, DOFs 2512A, 2512B, 2514, 2516,2518A, 2518B are used to kinematically support the side plate 2504A. TheDOF 2514 is “borrowed” from a payload assembly 2506 (or other structuralelement) to create a kinematic support condition. The side plate 2504Ais also attached to the base plate 2502 via redundant DOFs 2520A-2520B.The redundant DOFs 2520A, 2520B may be allowable because theirdirections support the attached plates 2504A-2504B in DOFs that have anassociated soft stiffness of plate out-of-plane bending. The redundantDOFs 2520A, 2520B may therefore preserve the flatness in both the baseplate 2502 and the side plate 2504A.

In other embodiments, it may be desirable to have a degenerate or aredundant support system for a C-type or L-type megastack structure2500. If a degenerate support system is desired, the megastack structure2500 may support and/or align the payload assembly 2506 using less thanthree attachment points 2510. If a redundant support system is desired,the megastack structure 2500 may support and/or align the payloadassembly 2506 using more than three attachment points 2510.

The attachment points 2510A-2510C (FIG. 25) are geometrically positionedsuch that two attachment points 2510A and 2510C are elevated above thebase plate 2502, and one attachment point 2510B is in the plane of thebase plate 2502. This geometrical attachment arrangement, or othersimilar arrangements, when combined with the specific directions oflocal DOF support, produce a non-degenerate, non-redundant,pseudo-kinematic support for a payload plate 2506.

As another example, an L-type megastack may have two attachments pointson a base plate and one attachment point elevated above the baseplateplane on a sideplate. Here the local DOF supported at each attachmentpoint are in different directions from the pictured C-type megastack2500 in FIG. 25.

FIG. 26 is an enlarged view of some attachment points 2510A, 25101B ofthe side plate 2504A and the base plate 2502 in FIG. 25. Given thegeometric position of the attachment points 2510A-2510C (FIG. 25), aC-type megastack payload assembly structure 2506 is pseudo-kinematicallysupported by two precisely-controlled DOFs 2602A, 2602B (FIG. 26) fromattachment point 2510A, two DOFs 2604A, 2604B from attachment point2510B, and two DOFs (not shown) from attachment point 2510C (FIG. 25).The two DOFs (not shown) from attachment point 2510C are similar to thetwo DOFs 2602A, 2602B (FIG. 26) from attachment point 2510A.

In FIGS. 25 and 26, flexure systems with integral preloaders 2606A,2606B, 2608A, 2808B may be implemented for maximum positioningprecision. For example, preloader 2608B preloads a tapered tab (notshown) of a payload assembly 2506 to seat the tab against the slot25101B in DOF 2604A, which forms a tab-in-slot configuration as shown inFIGS. 9 and 11. Preloader 2608A may use a tapered pin (not shown) topreload the tab (not shown) of a payload assembly 2506 against the slot2510B in DOF 2604B. Similarly, the preloaders 2606A, 2606B may preload atab, such as tab 2610, in DOFs 2602B, 2602A, respectively. The tab 2610may have a preloader 2612.

FIG. 27 is the top view of the megastack structure 2500 in FIG. 25.

FIG. 28 is the side view schematic of one embodiment of a side plate,such as the sideplate 2504A in FIG. 25. The side plate 2802 in FIG. 28is another example of planar positioning accuracy. The side plate 2802has three slots 2804A-2804C for engaging three tabs 2806A-2806C of threepayload assemblies, such as the payload wafer 2506 in FIG. 25. In FIG.28, the slots 2804A-2804C are open-ended at a top side. In FIG. 25, theside plates 2504A, 2504B have slots 2510A, 2510B that are closed-endedat all sides and form a window opening in the side plates 2504A, 2504B.Similarly, the base 2502 in FIG. 25 has slots 2510B that areclosed-ended at all sides and form a window opening in the base assembly2502.

The side plate 2802 in FIG. 28 may precisely control two DOFs on each ofthe three tabs 2806A-2806C of attached payload wafers (FIG. 25). Thevertical edges 2810A-2810C of the slots 2804A-2804C may allow precisedefinition of the horizontal separation 2808A, 2808B between the threetabs 2806A-2806C (even more precise if the tabs 2806A-2806C arepreloaded against the slots 2810A-2810C). The horizontal (bottom) edgesof the slots 2804A-2804C provide a vertical reference between the tabs2806A-2806C (again, even more precise when the tabs 2806A-2806C arepreloaded against the bottom edges).

The side plate 2802 in FIG. 28 may be used in conjunction with one ortwo other similar objects (each appropriately connected to the others)to completely define the positions and orientations of three payloadwafers, which each have a plurality of tabs (FIG. 28 shows tabs2806A-2806C of three payload wafers).

In some applications, it is desirable to have the side plate 2802 withslots 2804A-2804C that are equidistant from one another, as shown bydistances 2808A-2808B. An equidistant arrangement may allow properalignment of the payload assemblies.

FIG. 29 is a three-dimensional view of a complete megastack structure2900, which is shown partially in FIG. 25, with a plurality of payloadassemblies 2902A-2902G. The complete megastack structure 2900 in FIG. 29comprises side plates 2504A, 2504B, a base plate 2502, tabs (such as tab2610), slots, internal flexure assemblies, payload assemblies2902A-2902G, optical elements (collectively referred to as“components”), as described above. The attachment mechanisms maintainthe complete megastack structure 2900 in a pseudo-kinematic state.

FIG. 30 is a three-dimensional bottom view of the complete megastackstructure 2900 in FIG. 29. FIG. 30 shows one side plate 2504B, the baseplate 2502, one payload assembly 2506, bottom tabs 3002A-3002C of theside plate 2504B and bottom tabs 3004A-3004C of three payloadassemblies. The bottom tabs 3002A-3002C and bottom tabs 3004A-3004Cprotrude from the bottom surface of the base plate 2502.

The complete megastack structure 2900 in FIGS. 29 and 30 may befabricated using the same manufacturing procedures described herein. Forexample, using the lithography process and the micromachining process tofabricate the tabs, slots, internal flexure assemblies, payloadassemblies, sideplate assemblies, and base assemblies.

FIG. 31 illustrates one method of designing the three-dimensionalstructures and assemblies described above and translating the designsinto masks for high precision microlithography/photolithography. Theactions described in FIG. 31 may be performed in the order as shown orin alternative orders. Some of the actions may be skipped or combinedwith other actions. The method of FIG. 31 may include other actions inaddition to or instead of the actions shown.

FIG. 32 illustrates one method of making high precision,three-dimensional structures described above. The actions described inFIG. 32 may be performed in the order as shown or in alternative orders.Some of the actions may be skipped or combined with other actions. Themethod of FIG. 32 may include other actions in addition to or instead ofthe actions shown.

FIG. 33 illustrates one method of assembling three-dimensionalstructures described above from planar parts. The actions described inFIG. 33 may be performed in the order as shown or in alternative orders.Some of the actions may be skipped or combined with other actions. Themethod of FIG. 33 may include other actions in addition to or instead ofthe actions shown.

The above-described embodiments of the present invention are merelymeant to be illustrative and not limiting. Various changes andmodifications may be made without departing from the invention in itsbroader aspects. The appended claims encompass such changes andmodifications within the spirit and scope of the invention.

What is claimed is:
 1. An assembly configured to support at least oneoptical element to a pre-determined position, the assembly comprising: afirst micromachined structure having three protrusions, each protrusionhaving a pre-determined height; and a second micromachined structurehaving three grooves, each groove having a pre-determined depth, thedepth of each groove being less than a height of each protrusion, eachgroove being configured to contact one of the protrusions and controlthe protrusion in two degrees of freedom when a preload is applied tothe assembly, the grooves and protrusions being configured to constrainthe second micromachined structure in only six degrees of freedom withrespect to the first micromachined structure, the second micromachinedstructure being configured to support at least one optical element. 2.The assembly of claim 1, wherein the assembly comprises a passivealignment assembly.
 3. The assembly of claim 1, wherein the secondmating part is configured to contact the first mating part to constrainthe second micromachined structure with respect to the firstmicromachined structure in six degrees of freedom, the six constraineddegrees of freedom comprising: three orthogonal translational positionsconstrained to less than one micron; and three orthogonal angularposition constrained to less than five arcseconds.
 4. The assembly ofclaim 1, wherein the first and second micromachined structures arefabricated using a lithographic micromachining process.
 5. The assemblyof claim 1, wherein the first micromachined structure is also configuredto support at least one optical element.
 6. The assembly of claim 5,wherein a first optical element supported by the first micromachinedstructure is aligned with a second optical element supported by thesecond micromachined structure.
 7. The assembly of claim 1, wherein thesecond micromachined structure is configured to position the opticalelement with respect to the first micromachined structure.
 8. Theassembly of claim 1, wherein the first micromachined structure comprisesa substrate with at least a first receptacle, the second micromachinedstructure comprises a substrate with at least a second receptacle, thepairing of the first receptacle and the second of receptacle beingconfigured to align an optical element with about six constraineddegrees of freedom.
 9. The assembly of claim 1, wherein the opticalelement is an optical fiber.
 10. The assembly of claim 1, wherein theoptical element is a lens.
 11. The assembly of claim 1, wherein theoptical element is a mirror.
 12. The assembly of claim 1, wherein theoptical element is a diode.
 13. The assembly of claim 1, wherein thefirst and second micromachined structures are formed from substantiallyflat silicon wafers.
 14. The assembly of claim 1, wherein the first andsecond micromachined structures comprise substantially planar wafers.15. The assembly of claim 1, wherein the first mating part and thesecond mating part comprise a plurality of slip-fit joint assemblies.16. The assembly of claim 1, wherein the first mating part comprises aplurality of slots and the second mating part comprises a plurality oftabs configured to fit into the slots.
 17. The assembly of claim 1,wherein the first micromachined structure comprises a rib, the firstmating part comprises a plurality of attachment points and the secondmating part comprises a plurality of slots configured to receive theattachment points.
 18. The assembly of claim 17, wherein the attachmentpoints comprise tabs.
 19. An assembly configured to support at least oneoptical element, the assembly comprising: a first micromachinedstructure having three protrusions, each protrusion having foursidewalls, each sidewall being substantially perpendicular to a plane ofthe first micromachined structure, each protrusion having a sidewallfacing a center point of the first micromachined structure; and a secondmicromachined structure having three grooves, the grooves beingconfigured to contact the protrusions to restrain the secondmicromachined structure with respect to the first micromachinedstructure in six degrees-of-freedom (DOFs), the second micromachinedstructure being configured to support at least one optical element at apre-determined position.
 20. The assembly of claim 19, wherein thesecond micromachined structure is restrained with respect to the firstmicromachined structure with glue.